The malfunctioning of protein kinases (PKs) is the hallmark of numerous diseases. A large share of the oncogenes and proto-oncogenes involved in human cancers encode for PKs. The enhanced activities of PKs are also implicated in many non-malignant diseases, such as benign prostate hyperplasia, familial adenomatosis, polyposis, neuro-fibromatosis, psoriasis, vascular smooth cell proliferation associated with atherosclerosis, pulmonary fibrosis, arthritis, glomerulonephritis and post-surgical stenosis and restenosis.
PKs are also implicated in inflammatory conditions and in the multiplication of viruses and parasites. PKs may also play a major role in the pathogenesis and development of neurodegenerative disorders.
For a general reference to PKs malfunctioning or deregulation see, for instance, Current Opinion in Chemical Biology 1999, 3, 459-465; Nature Rev. Drug Discov. 2002; and Carcinogenesis 2008, 29, 1087-1091.
A subset of PK is a group of membrane receptors with intrinsic protein-tyrosine kinase activity (RPTK). Upon binding of growth factors, RPTKs become activated and phosphorylate themselves and a series of substrates in the cytoplasm. Through this mechanism, they can transduce intracellular signallings for proliferation, differentiation or other biological changes. Structural abnormalities, over-expression and activation of RPTKs are frequently observed in human tumors, suggesting that constitutive ignition of the signal transduction leading to cell proliferation can result in malignant transformation. Anaplastic lymphoma kinase (ALK) is a tyrosine kinase receptor belonging to the insulin receptor subfamily of RPTKs: the ALK gene is located on cromosome 2 and is expressed mainly in neuronal cells, especially during development. The ALK gene is involved in a balanced chromosomal translocation with the Nucleophosmin (NPM) gene on cromosome 5 in a large subset of Anaplastic Large Cell Lymphomas (ALCL). In the ALK+ ALCL, as a result of the translocation, the NPM ubiquitous promoter drives an ectopic expression of the fusion protein in which the NPM moiety dimerizes and the ALK kinase domain undergoes auto-phosphorylation and becomes constitutively active.
Many data from the literature have demonstrated that the NPM-ALK fusion protein has a strong oncogenic potential and its ectopic expression is responsible for cellular transformation. Moreover, the constitutive expression of human NPM-ALK in mouse T-cell lymphocytes is sufficient for the development of lymphoid neoplasia in transgenic animals with a short period of latency.
ALCL is a defined disease characterized by the surface expression of the CD30 antigen (Ki-1), and accounts for 2% of adult and 13% of pediatric non-Hodgkin's lymphomas, affecting predominantly young male patients. ALK+ ALCL accounts for 70% of all ALCLs and is an aggressive disease with systemic signs, and frequent extranodal involvement (bone marrow, skin, bone, soft tissues).
About 15-20% of ALK-expressing ALCLs were found to bear a different chromosomal translocation, involving the cytoplasmic portion of ALK, with different N-terminal moieties, all resulting in constitutive activation of the ALK kinase domain.
Moreover, cell lines established from solid tumors of ectodermal origin like melanomas, breast carcinomas, as well as neuroblastomas, glioblastomas, Ewings sarcomas, retinoblastomas, were found to express the ALK receptor.
ROS1 belongs to the insulin-receptor superfamily. Like other tyrosine kinase receptor molecules, it plays a role in relaying growth signals from the environment outside the cell into the cell's nucleus. It is 1 of 2 orphan receptor tyrosine kinase family members with no known binding ligand. Genetic changes in ROS1, such as gene rearrangements, mutations, or copy number increases, create oncogenes, which can lead to cancer (Stumpfova and Janne, 2012). ROS1 was discovered in NSCLC patients in the form of a fusion protein (6 different partners for ROS1) and is found in approximately 2% of patients with NSCLC (Bergethon et al., 2012; Davies et al, 2012). Two other ROS1 gene rearrangements have been detected in a variety of other cancers, including glioblastoma multiforme, cholangiocarcinoma, ovarian cancer, gastric adenocarcinoma, colorectal cancer, inflammatory myofibroblastic tumor, angiosarcoma, and epitheloid hemangioendothelioma (Lee et al., 2013; Davies and Doebele, 2013; Davies, et al., 2012; Shaw et al., 2013).
ROS1 gene rearrangements create fusion proteins with constitutively active kinase domains that activate downstream signaling pathways leading to oncogenic properties in cells, including uncontrolled proliferation and resistance to cell death with prolonged tumor cell survival. These pathways include Ras-ERK for cellular proliferation and the JAK-STAT and PI3K/AKT pathways, which regulate cell survival (anti-apoptosis) and proliferation. ROS1 fusion proteins may also activate the mTOR pathway, which is critical for the regulation of protein translation. Cancers that have these pathways activated tend to be more aggressive, with invasion and metastasis leading to poor survival of the patients (Davies and Doebele, 2013).
Trk's are the high affinity receptor tyrosine kinases activated by a group of soluble growth factors called neurotrophins (NT). The Trk receptor family has three members—TrkA, TrkB and TrkC. Among the neurotrophins are (i) nerve growth factor (NGF) which activates TrkA, (ii) brain-derived neurotrophic factor (BDNF) and NT-4/5 which activate TrkB and (iii) NT3 which activates TrkC. Trk's are widely expressed in neuronal tissue and are implicated in the maintenance, signaling and survival of neuronal cells (Patapoutian, A. et al., Current Opinion in Neurobiology, 2001, 11, 272-280). NTRK1 encodes the TrkA receptor tyrosine kinase. TrkA activates the PI3K/AKT, PKC and ERK1/2 pathways which promote cell growth and survival.
Recent literature has also shown that overexpression, activation, amplification and/or mutation of Trk's are associated with many cancers including neuroblastoma (Brodeur, G. M., Nat. Rev. Cancer 2003, 3, 203-216), ovarian cancer (Davidson. B., et al., Clin. Cancer Res. 2003, 9, 2248-2259), breast cancer (Kruettgen et al, Brain Pathology 2006, 16: 304-310), prostate cancer (Dionne et al, Clin. Cancer Res. 1998, 4(8): 1887-1898), pancreatic cancer (Dang et al, Journal of Gastroenterology and Hepatology 2006, 21(5): 850-858), multiple myeloma (Hu et al, Cancer Genetics and Cytogenetics 2007, 178: 1-10), astrocytoma and medulloblastoma (Kruettgen et al, Brain Pathology 2006, 16: 304-310) glioma (Hansen et al, Journal of Neurochemistry 2007, 103: 259-275), melanoma (Truzzi et al, Journal of Investigative Dermatology 2008, 128(8): 2031-2040, thyroid carcinoma (Brzezianska et al, Neuroendocrinology Letters 2007, 28(3), 221-229.), lung adenocarcinoma (Perez-Pinera et al, Molecular and Cellular Biochemistry 2007, 295(1&2), 19-26), large cell neuroendocrine tumors (Marchetti et al, Human Mutation 2008, 29(5), 609-616), and colorectal cancer (Bardelli, A., Science 2003, 300, 949). In preclinical models of cancer, Trk inhibitors are efficacious in both inhibiting tumor growth and stopping tumor metastasis. In particular, non-selective small molecule inhibitors of Trk A, B and C and Trk/Fc chimeras were efficacious in both inhibiting tumor growth and stopping tumor metastasis (Nakagawara, A. (2001) Cancer Letters 169:107-114; Meyer, J. et al. (2007) Leukemia, 1-10; Pierotti, M. A. and Greco A., (2006) Cancer Letters 232:90-98; Eric Adriaenssens, E. et al. Cancer Res (2008) 68:(2) 346-351) (Truzzi et al, Journal of Investigative Dermatology 2008, 128(8): 2031-2040. Therefore, an inhibitor of the Trk family of kinases is expected to have utility in the treatment of cancer.
In conclusion, interfering with ALK or ROS1 signaling likely represents a specific and effective way to block tumor cell proliferation in ALCL and possibly other indications. The insulin-like growth factor 1 receptor (IGF-1R, IGF1R) is also a member of the insulin receptor subfamily of RTKs. In addition, interfering with TrkA, TrkB and/or TrkC signaling, or a combination thereof, represents a specific and effective way to block tumor cell proliferation in various cancers, including, but not limited to, non-small cell lung cancer, papillary thyroid cancer, neuroblastoma, pancreatic cancer and colorectal cancer.